JP7272372B2 - Epoxy resin B-stage film, epoxy resin cured film, and method for producing epoxy resin cured film - Google Patents

Description

The present invention relates to an epoxy resin B-stage film, an epoxy resin cured film, and a method for producing an epoxy resin cured film.

In recent years, the amount of heat generated per unit volume tends to increase as the energy density increases due to the miniaturization and performance enhancement of electronic devices. there is Epoxy resin is widely used as an insulating material from the viewpoint of high withstand voltage and ease of molding. As a method for increasing the thermal conductivity of epoxy resin, a method of adding a filler having high thermal conductivity and insulating property to the resin is generally used. Alumina particles and the like are examples of fillers having high thermal conductivity and insulating properties.
By combining liquid crystalline epoxy resin and alumina particles, the liquid crystalline epoxy resin forms a higher-order structure on the alumina surface, and the higher-order structure forms a thermal conduction path that connects the alumina particles, increasing thermal conductivity. That is described in WO2013/065758.
Furthermore, as an insulating composition having electrical insulation and excellent thermal conductivity, an insulating composition containing as an essential component a liquid crystalline resin obtained by polymerizing a resin composition containing a monomer having a mesogenic group is disclosed in JP-A-11- 323,162. Japanese Patent Application Laid-Open No. 11-323162 describes that an insulating composition may contain an inorganic ceramic having excellent thermal conductivity such as aluminum oxide.

However, it may not be possible to form a thin film by the method of filling an insulating filler. Development of a material that is excellent in thermal conductivity even in a thin film is desired.
In view of the above situation, an object of the present invention is to provide an epoxy resin B-stage film capable of forming an epoxy resin cured film having excellent thermal conductivity, an epoxy resin cured film having excellent thermal conductivity, and a method for producing the epoxy resin cured film. to do.

Specific means for solving the above problems are as follows.
<1> A semi-cured epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent,
an average thickness of less than 8 μm,
An epoxy resin B-stage film which, when cured, has a liquid crystal structure in which the molecules are oriented in the direction of film thickness.
<2> The epoxy resin B-stage film according to <1>, wherein the liquid crystalline epoxy monomer contains a monomer represented by the following general formula (I).

[In general formula (I), R ¹ to R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ]
<3> The epoxy resin according to <2>, wherein the liquid crystalline epoxy monomer contains a reaction product of the monomer represented by the general formula (I) and at least one selected from the group consisting of hydroquinone and biphenol. B stage film.
<4> The epoxy resin B-stage film according to any one of <1> to <3>, wherein the curing agent contains an amine curing agent.
<5> A cured epoxy resin film having a liquid crystal structure in which molecules are oriented in the thickness direction of the film and having an average thickness of less than 8 μm.
<6> The cured epoxy resin film according to <5>, wherein the liquid crystal structure is a nematic structure or a smectic structure.
<7> The epoxy resin cured film according to <5> or <6>, which is a cured product of an epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent.
<8> The epoxy resin cured film according to <7>, wherein the liquid crystalline epoxy monomer contains a monomer represented by the following general formula (I).

[In general formula (I), R ¹ to R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ]
<9> The epoxy resin according to <8>, wherein the liquid crystalline epoxy monomer contains a reaction product of the monomer represented by the general formula (I) and at least one selected from the group consisting of hydroquinone and biphenol. curing film.
<10> The epoxy resin cured film according to any one of <7> to <9>, wherein the curing agent contains an amine curing agent.
<11> The epoxy resin cured film according to <5> or <6>, which is a cured product of the epoxy resin B-stage film according to any one of <1> to <4>.
<12> forming a film having an average thickness of less than 8 μm at 150° C. or less using an epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent;
curing the film at a curing temperature of 200° C. or less;
A method for producing an epoxy resin cured film having

According to the present invention, it is possible to provide an epoxy resin B-stage film capable of forming a cured epoxy resin film having excellent thermal conductivity, a cured epoxy resin film having excellent thermal conductivity, and a method for producing a cured epoxy resin film.

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present invention.
In the present disclosure, the term "process" includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
In the present disclosure, the numerical range indicated using "-" includes the numerical values before and after "-" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
In the present disclosure, each component may contain multiple types of applicable substances. When there are multiple types of substances corresponding to each component in the composition, the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
Particles corresponding to each component in the present disclosure may include a plurality of types. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In the present disclosure, the term "film" includes not only the case where the film is formed in the entire region when observing the region where the film exists, but also the case where it is formed only in part of the region. included.
In the present disclosure, the average thickness is a value given as the arithmetic mean value of five randomly selected thicknesses of an object. The thickness can be measured using a micrometer or the like.

<Epoxy resin B stage film>
The epoxy resin B-stage film of the present disclosure (hereinafter sometimes simply referred to as "B-stage film") is an epoxy resin containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent. A film obtained by semi-curing a resin composition, having an average thickness of less than 8 μm, and having a liquid crystal structure in which molecules are oriented in the thickness direction of the film by curing. is.
It is believed that the B-stage film having the above structure improves the thermal conductivity of the cured product of the B-stage film. The B-stage film may further contain other components.
In the present disclosure, the definition of JIS K6900:1994 shall be referred to for "A stage" and "B stage". Since the unreacted liquid crystalline epoxy monomer and curing agent remain in the B-stage film, the B-stage film can be cured by heating.
In the present disclosure, "semi-curing" the epoxy resin composition means heating the epoxy resin composition to advance the reaction to the B stage.

The average thickness of the B-stage film is less than 8 μm, preferably 7 μm or less, more preferably 6 μm or less, and even more preferably 5 μm or less.

The components of the epoxy resin composition, which is the basis of the epoxy resin B-stage film, will be described in detail below.
The epoxy resin composition used in the present disclosure contains a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure, a curing agent, and optionally other components.

(Liquid crystalline epoxy monomer)
The epoxy resin composition contains a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure. Such liquid crystalline epoxy monomers include, for example, a mesogenic structure (biphenyl group, cyclohexylphenyl group, terphenyl group, terphenyl-related group, anthracene group, a group in which these are connected by an azomethine group or an ester group, etc.). monomers. When a liquid crystalline epoxy monomer having a mesogenic structure reacts with a curing agent to form a cured product (sometimes referred to as a resin matrix), a higher-order structure (also referred to as a periodic structure) derived from the mesogenic structure is formed in the resin matrix. It is formed.

A higher-order structure (periodic structure) as used in the present disclosure means a state in which molecules are oriented in a resin matrix, for example, a state in which a crystal structure or a liquid crystal structure exists in the resin matrix. The presence of such a crystal structure or liquid crystal structure can be directly confirmed, for example, by observation with a polarizing microscope under crossed Nicols or by X-ray scattering. In addition, if a crystal structure or liquid crystal structure exists, the change in the storage modulus of the resin with respect to temperature becomes small, so by measuring the change in this storage modulus with respect to temperature, the existence of the crystal structure or liquid crystal structure can be indirectly confirmed. can.

A highly regular higher-order structure derived from a mesogenic structure includes a nematic structure, a smectic structure, and the like. A nematic structure is a liquid crystal structure in which the molecular long axes are oriented in a uniform direction and only orientational order exists. On the other hand, the smectic structure is a liquid crystal structure that has a one-dimensional positional order in addition to the orientational order and has a layered structure with a constant period. In addition, within the same periodic structure of the smectic structure, the direction of the periodicity of the layered structure is uniform. The liquid crystal structure is preferably nematic or smectic.
In addition, the ratio of the liquid crystal structure to the entire resin matrix can be easily measured, for example, by observing with a polarizing microscope. Specifically, the cured product is observed with a polarizing microscope (for example, manufactured by Nikon Corporation, product name: "OPTIPHOT2-POL") to measure the area of the liquid crystal structure, and the percentage of the area of the entire field of view observed with the polarizing microscope. By obtaining , the ratio of the liquid crystal structure to the entire resin matrix can be easily measured.

From the viewpoint of forming a liquid crystal structure, the liquid crystalline epoxy monomer preferably contains a monomer represented by the following general formula (I). Monomers represented by the following general formula (I) may be used singly or in combination of two or more.

In general formula (I), R ¹ to R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. R ¹ to R ⁴ are each independently preferably a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, more preferably a hydrogen atom or a methyl group, even more preferably a hydrogen atom. In addition, 2 to 4 of R ¹ to R ⁴ are preferably hydrogen atoms, more preferably 3 or 4 are hydrogen atoms, and further preferably all 4 are hydrogen atoms. preferable. When any one of R ¹ to R ⁴ is an alkyl group having 1 to 3 carbon atoms, at least one of R ¹ and R ⁴ is preferably an alkyl group having 1 to 3 carbon atoms.

Examples of the monomer represented by formula (I) are described in JP-A-2011-74366, for example. Specifically, monomers represented by general formula (I) include, for example, 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate and 4- and {4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)-3-methylbenzoate.

Other liquid crystalline epoxy monomers include, for example, biphenyl epoxy monomers and tricyclic epoxy monomers other than the monomers represented by general formula (I).

Biphenyl-type epoxy monomers include 4,4′-bis(2,3-epoxypropoxy)biphenyl, 4,4′-bis(2,3-epoxypropoxy)-3,3′,5,5′-tetramethyl Epoxy monomers obtained by reacting biphenyl, epichlorohydrin with α-hydroxyphenyl-ω-hydropoly(biphenyldimethylene-hydroxyphenylene), and the like. Biphenyl-type epoxy resins include product names such as "YX4000", "YL6121H" (manufactured by Mitsubishi Chemical Corporation), "NC-3000", and "NC-3100" (manufactured by Nippon Kayaku Co., Ltd.). Commercially available products can be mentioned.

Examples of tricyclic epoxy monomers include epoxy monomers having a terphenyl skeleton, 1-(3-methyl-4-oxiranylmethoxyphenyl)-4-(4-oxiranylmethoxyphenyl)-1-cyclohexene, 1- (3-methyl-4-oxiranylmethoxyphenyl)-4-(4-oxiranylmethoxyphenyl)-benzene and the like.

Liquid crystalline epoxy monomers include 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate or 1-(3-methyl-4-oxiranylmethoxyphenyl )-4-(4-oxiranylmethoxyphenyl)-1-cyclohexene is preferred.

At least part of the liquid crystalline epoxy monomer may be in a prepolymer state obtained by reacting with a prepolymerizing agent described below. The prepolymerizing agent is a compound having a functional group capable of reacting with the epoxy group of the liquid crystalline epoxy monomer and capable of polymerizing the liquid crystalline epoxy monomer to form a prepolymer.
Liquid crystalline epoxy monomers having a mesogenic structure in the molecular structure, including the monomer represented by general formula (I), are generally easy to crystallize, and many of them have lower solubility in solvents than other epoxy monomers. By polymerizing at least part of the liquid crystalline epoxy monomer to form a prepolymer, crystallization tends to be suppressed and the moldability of the epoxy resin composition tends to be improved.

The prepolymerizing agent may be the same as or different from the curing agent described below. Specifically, the prepolymerizing agent is a dihydric phenol compound having two hydroxyl groups as substituents on one benzene ring, or a biphenol compound having two hydroxyl groups as substituents on two benzene rings. catechol, resorcinol, hydroquinone, derivatives thereof, biphenols such as 3,3′-biphenol and 4,4′-biphenol, and derivatives thereof. Derivatives include compounds in which a benzene ring is substituted with an alkyl group having 1 to 8 carbon atoms or the like. Among these prepolymerizing agents, it is preferable to use at least one selected from the group consisting of hydroquinone, 3,3'-biphenol and 4,4'-biphenol from the viewpoint of improving the thermal conductivity of the molded product. , 4,4'-biphenol is more preferably used. Since 4,4'-biphenol has a structure in which two hydroxyl groups are substituted so as to have a positional relationship of point symmetry, the prepolymer obtained by reacting it with a liquid crystalline epoxy monomer tends to have a linear structure. For this reason, it is considered that the molecular stacking property is high and a higher-order structure is likely to be formed.
These prepolymerizing agents may be used singly or in combination of two or more.

In the present disclosure, the liquid crystalline epoxy monomer preferably contains, as a prepolymer, a reaction product of a monomer represented by general formula (I) and at least one selected from the group consisting of hydroquinone and biphenol. More preferably, it contains a reaction product of at least one selected from the group consisting of the monomer represented by formula (I) and hydroquinone, 3,3'-biphenol and 4,4'-biphenol as a prepolymer, More preferably, the prepolymer comprises a reaction product of a monomer represented by general formula (I) and 4,4'-biphenol.

The prepolymer is obtained by blending and reacting a liquid crystalline epoxy monomer and a prepolymerization agent so that the equivalent ratio of epoxy groups and hydroxyl groups (epoxy group/hydroxyl group) is 100/5 to 100/35. This equivalent ratio is more preferably 100/15 to 100/30, even more preferably 100/15 to 100/25.

The method of synthesizing the prepolymer by reacting the liquid crystalline epoxy monomer and the prepolymerizing agent is not particularly limited. Specifically, for example, a prepolymer can be synthesized by dissolving a liquid crystalline epoxy monomer, a prepolymerization agent, and an optional reaction catalyst in a solvent and stirring the solution while heating.
Alternatively, a prepolymer can be synthesized by mixing a liquid crystalline epoxy monomer, a prepolymerization agent, and an optional reaction catalyst without using a solvent and stirring the mixture while heating.

The solvent is not particularly limited as long as it can dissolve the liquid crystalline epoxy monomer and the prepolymerizing agent and can be heated to a temperature necessary for the two compounds to react. Specific examples include cyclohexanone, cyclopentanone, ethyl lactate, propylene glycol monomethyl ether, N-methylpyrrolidone, methyl cellosolve, ethyl cellosolve, propylene glycol monopropyl ether and the like.

The amount of the solvent is not particularly limited as long as it can dissolve the liquid crystalline epoxy monomer, the prepolymerization agent and the optional reaction catalyst at the reaction temperature. Although the solubility varies depending on the type of raw material before the reaction, the type of solvent, etc., for example, if the concentration of solids charged is 20% by mass to 60% by mass, the viscosity of the solution after the reaction is in a preferable range. There is a tendency.

The type of reaction catalyst is not particularly limited, and an appropriate one can be selected from the viewpoint of reaction rate, reaction temperature, storage stability, and the like. Specific examples include imidazole compounds, organic phosphorus compounds, tertiary amines, quaternary ammonium salts and the like. One type of the reaction catalyst may be used alone, or two or more types may be used in combination.

The amount of reaction catalyst is not particularly limited. From the viewpoint of reaction rate and storage stability, it is preferably 0.1 to 1.5 parts by mass, and 0.2 parts by mass, per 100 parts by mass of the total mass of the liquid crystalline epoxy monomer and the prepolymerizing agent. It is more preferably from 1 part by mass to 1 part by mass.

When synthesizing a prepolymer using a liquid crystalline epoxy monomer, even if all of the liquid crystalline epoxy monomer reacts to form a prepolymer, part of the liquid crystalline epoxy monomer remains unreacted and remains in the form of a monomer. It may remain in the prepolymer.

The synthesis of the prepolymer can be carried out using a reaction vessel such as a flask for small-scale synthesis and a synthesis tank for large-scale synthesis. A specific synthesis method is, for example, as follows.
First, a liquid crystalline epoxy monomer is put into a reaction vessel, a solvent is added if necessary, and the liquid crystalline epoxy monomer is dissolved by heating to the reaction temperature with an oil bath or a heat medium. A prepolymerization agent is added thereto, and then, if necessary, a reaction catalyst is added to initiate the reaction. Then, if necessary, the prepolymer is obtained by distilling off the solvent under reduced pressure.

The reaction temperature is not particularly limited as long as the reaction between the epoxy group of the liquid crystalline epoxy monomer and the functional group capable of reacting with the epoxy group of the prepolymerizing agent proceeds. It is preferably in the range of 100°C to 150°C. Setting the reaction temperature to 100° C. or higher tends to shorten the time until the reaction is completed. On the other hand, setting the reaction temperature to 180° C. or lower tends to reduce the possibility of gelation.

From the viewpoint of moldability, the content of the liquid crystalline epoxy monomer is preferably 5% to 80% by volume, more preferably 10% to 70% by volume, based on the total solid content of the epoxy resin composition. It is preferably 20% by volume to 60% by volume, and particularly preferably 30% by volume to 50% by volume.

In the present disclosure, the volume-based content ratio of the liquid crystalline epoxy monomer to the total solid content is a value obtained by the following formula.
Content of liquid crystalline epoxy monomer relative to total solid content (% by volume)=[(Bw/Bd)/{(Aw/Ad)+(Bw/Bd)+(Cw/Cd)+(Dw/Dd)}]× 100
Here, each variable is as follows.
Aw: Mass composition ratio (% by mass) of filler used as necessary
Bw: Mass composition ratio of liquid crystalline epoxy monomer (% by mass)
Cw: Mass composition ratio of curing agent (% by mass)
Dw: Mass composition ratio (% by mass) of other optional components (excluding solvent)
Ad: Specific gravity of filler used as necessary Bd: Specific gravity of liquid crystalline epoxy monomer Cd: Specific gravity of curing agent Dd: Specific gravity of other optional components (excluding solvent)

The epoxy resin composition may further contain other epoxy monomers than the liquid crystalline epoxy monomer. Other epoxy monomers include glycidyl ethers of phenolic compounds such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolac, and resorcinol novolak; glycidyl ethers of alcohol compounds such as butanediol, polyethylene glycol, and polypropylene glycol; phthalic acid. , isophthalic acid, glycidyl esters of carboxylic acid compounds such as tetrahydrophthalic acid; glycidyl-type (including methylglycidyl-type) epoxy monomers such as those in which active hydrogens bonded to nitrogen atoms such as aniline and isocyanuric acid are substituted with glycidyl groups; Vinylcyclohexene epoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 2-(3,4-epoxy)cyclohexyl-5,5-spiro(3 ,4-epoxy)cyclohexane-m-dioxane; epoxidized bis(4-hydroxy)thioether; para-xylylene-modified phenol resin, meta-xylylene-para-xylylene-modified phenol resin, terpene-modified phenol resin, di Glycidyl ethers such as cyclopentadiene-modified phenolic resin, cyclopentadiene-modified phenolic resin, polycyclic aromatic ring-modified phenolic resin, naphthalene ring-containing phenolic resin; stilbene-type epoxy monomers; (excluding reactive epoxy monomers). Other epoxy monomers may be used singly or in combination of two or more.

The content of other epoxy monomers is not particularly limited. .1 or less is more preferable.

(curing agent)
The epoxy resin composition contains a curing agent. The curing agent is not particularly limited as long as it is a compound capable of curing reaction with the liquid crystalline epoxy monomer. Specific examples of curing agents include amine curing agents, acid anhydride curing agents, phenol curing agents, polymercaptan curing agents, polyaminoamide curing agents, isocyanate curing agents, blocked isocyanate curing agents, and the like. These curing agents may be used alone or in combination of two or more.

From the viewpoint of the transparency of the cured product of the epoxy resin composition, the curing agent is preferably an amine curing agent or a phenol curing agent, more preferably an amine curing agent.

Specific examples of amine curing agents include 3,3′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 4,4′-diamino- 3,3'-dimethoxybiphenyl, 4,4'-diaminophenyl benzoate, 1,5-diaminonaphthalene, 1,3-diaminonaphthalene, 1,4-diaminonaphthalene, 1,8-diaminonaphthalene, 1,3-diamino Benzene, 1,4-diaminobenzene, 4,4'-diaminobenzanilide, trimethylene-bis-4-aminobenzoate and the like.

When a phenol curing agent is used as the curing agent, a curing accelerator may be used in combination as necessary. By using a curing accelerator together, the epoxy resin composition can be cured more sufficiently. The type of curing accelerator is not particularly limited, and may be selected from commonly used curing accelerators. Curing accelerators include, for example, imidazole compounds, phosphine compounds, and borate salt compounds.

The content of the curing agent in the epoxy resin composition can be appropriately set in consideration of the type of curing agent to be blended and the physical properties of the liquid crystalline epoxy monomer.
Specifically, the number of equivalents of the functional group of the curing agent is preferably 0.005 to 5 equivalents, more preferably 0.01 to 3 equivalents, with respect to 1 equivalent of the epoxy group in the liquid crystalline epoxy monomer. is more preferred, and 0.5 to 1.5 equivalents is even more preferred. When the number of equivalents of the functional group of the curing agent is 0.005 equivalent or more with respect to one equivalent of the epoxy group, there is a tendency that the curing speed of the liquid crystalline epoxy monomer can be further improved. Further, when the number of equivalents of the functional group of the curing agent is 5 equivalents or less with respect to 1 equivalent of the epoxy group, there is a tendency that the curing reaction can be controlled more appropriately.

In addition, the chemical equivalent in the present disclosure, for example, when a phenol curing agent is used as a curing agent, represents the number of equivalents of the hydroxyl group of the phenol curing agent with respect to one equivalent of the epoxy group, and an amine curing agent is used as the curing agent. , represents the number of active hydrogen equivalents of the amine curing agent per equivalent of the epoxy group.

(filler)
The epoxy resin composition may contain fillers. As the filler, ceramic particles can be used from the viewpoint of thermal conductivity and insulation. Ceramic particles include alumina particles, silica particles, magnesium oxide particles, boron nitride particles, aluminum nitride particles, silicon nitride particles and the like. The filler preferably contains at least one selected from the group consisting of alumina particles, boron nitride particles, aluminum nitride particles and magnesium oxide particles, and more preferably contains alumina particles. The alumina particles preferably contain highly crystalline alumina particles, more preferably α-alumina particles.
Further, when the filler contains alumina particles, it is preferable from the viewpoint of thermal conductivity to form a periodic smectic structure in the cured product of the epoxy resin composition in a direction perpendicular to the surface of the alumina particles. .

The volume average particle size of the filler is preferably 0.01 μm to 1 μm from the viewpoint of thermal conductivity, and more preferably 0.01 μm to 0.1 μm from the viewpoint of transparency.

Here, the volume average particle size of the filler is measured using a laser diffraction method. Measurement by the laser diffraction method can be performed using a laser diffraction scattering particle size distribution analyzer (for example, LS230 manufactured by Beckman Coulter). The volume-average particle size of the filler in the epoxy resin composition, B-stage film, or cured epoxy resin film is measured by a laser diffraction scattering particle size distribution analyzer after the filler is extracted from the epoxy resin composition, B-stage film, or cured epoxy resin film. Measured using

Specifically, using an organic solvent, nitric acid, aqua regia, etc., the filler is extracted from the epoxy resin composition, the B-stage film, or the epoxy resin cured film, and the obtained filler is added to the dispersion medium by an ultrasonic dispersing machine. etc. to prepare a dispersion liquid. A volume cumulative distribution curve of this dispersion is measured by a laser diffraction scattering particle size distribution analyzer. When the volume cumulative distribution curve is drawn from the small diameter side, the particle diameter (D50) at which the cumulative 50% is obtained is determined as the volume average particle diameter. The volume average particle size of the filler is measured.

From the viewpoint of facilitating thinning of the epoxy resin composition, the filler content is preferably 20% by mass or less, more preferably 15% by mass or less, based on the total solid content of the epoxy resin composition. , is more preferably 10% by mass or less, particularly preferably 1% by mass or less, and extremely preferably 0.1% by mass or less. The epoxy resin composition may contain no filler.

(other ingredients)
The epoxy resin composition may further contain coupling agents, dispersants, elastomers, release agents, solvents and the like.
Solvents include acetone, isobutyl alcohol, isopropyl alcohol, isopentyl alcohol, ethyl ether, ethylene glycol monoethyl ether, xylene, cresol, chlorobenzene, isobutyl acetate, isopropyl acetate, isopentyl acetate, ethyl acetate, methyl acetate, cyclohexanol, cyclohexanone. , 1,4-dioxane, dichloromethane, styrene, tetrachloroethylene, tetrahydrofuran, toluene, normal hexane, 1-butanol, 2-butanol, methanol, methyl isobutyl ketone, methyl ethyl ketone, methylcyclohexanol, methylcyclohexanone, chloroform, carbon tetrachloride, 1 , 2-dichloroethane and the like, which are generally used in the production technology of various chemical products, can be used.

(Method for producing epoxy resin B stage film)
The B-stage film of the present disclosure can be produced, for example, by molding the epoxy resin composition described above to an average thickness of less than 8 μm and semi-curing it. Examples of methods for molding the epoxy resin composition to an average thickness of less than 8 μm include a bar coating method and a spin coating method. A spin coating method is preferable from the viewpoint of uniform molding. The spin speed of spin coating is not limited, and is preferably 50 to 5,000 rpm, more preferably 100 to 3,000 rpm, even more preferably 500 to 2,500 rpm.
Although the temperature for spin coating is not limited, it is preferably 150° C. or lower, more preferably 100° C. or lower so as to prevent excessive curing of the epoxy resin composition.

The method for semi-curing the molded article obtained by molding the epoxy resin composition to an average thickness of less than 8 μm is not particularly limited. You may semi-harden by heating a molded object. A high-temperature bath, a hot plate, and the like can be used as a heating device for the molded body.
In the case of using the spin coating method, the molded body may be semi-cured by adjusting the temperature and the spin coating time during the spin coating.

The B-stage film of the present disclosure is obtained by molding the above-described epoxy resin composition to an average thickness of less than 8 μm on an oxide substrate with good water wettability (also referred to as hydrophilic) such as a glass substrate or an alumina substrate. It may have been When a B-stage film formed on an oxide substrate with good wettability with water is cured, the liquid crystal structure contained in the cured product tends to become a liquid crystal structure in which molecules are oriented in the thickness direction of the film.

(Use of epoxy resin B stage film, etc.)
The B-stage film of the present disclosure has high molecular orientation and excellent thermal conductivity when cured. Therefore, the epoxy resin B-stage film of the present disclosure can be suitably used as a heat dissipation material for heat-generating electronic components mounted in various electrical and electronic devices.

<Epoxy resin cured film and its manufacturing method>
The cured epoxy resin film of the present disclosure includes a liquid crystal structure in which molecules are oriented in the thickness direction of the film and has an average thickness of less than 8 μm. Since the liquid crystal structure contained in the cured epoxy resin film is a liquid crystal structure in which the molecules are oriented in the thickness direction of the film, the cured epoxy resin film of the present disclosure has excellent thermal conductivity.
Whether or not the liquid crystal structure is such that the molecules are aligned in the thickness direction of the film can be examined by conoscopic observation with a polarizing microscope. Specifically, using a polarizing microscope (for example, manufactured by Nikon Corporation, product name: "OPTIPHOT2-POL"), the epoxy resin cured film is placed under crossed Nicols, and the dark field is observed by orthoscopic observation. If a Maltese cross can be observed by conoscopic observation, it indicates that the molecules are oriented in the thickness direction of the film.

The epoxy resin cured film of the present disclosure has an average thickness of less than 8 μm. By setting the average thickness of the cured epoxy resin film to less than 8 μm, the molecules are easily oriented in the thickness direction of the film, resulting in excellent thermal conductivity in the thickness direction. Further, by setting the average thickness of the cured epoxy resin film to less than 8 μm, the probability of defects such as disturbed molecular orientation is reduced, so that the thermal conductivity tends to be stably increased.

The epoxy resin cured film of the present disclosure may be a cured product obtained by curing the epoxy resin B-stage film of the present disclosure or the epoxy resin composition described above.
The epoxy resin cured film of the present disclosure is a film having an average thickness of less than 8 μm at 150° C. or less using an epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent. and a step of curing the film at a curing temperature of 200° C. or less (hereinafter sometimes referred to as a curing step). It may be obtained through the method for producing an epoxy resin cured film.
In the film forming step, the epoxy resin composition can be used to form a film by a bar coating method, a spin coating method, or the like. The film formed in the film forming step may be a B-stage film, or an A-stage film in which the liquid crystalline epoxy monomer contained in the film is not yet cured.

In order to form a liquid crystal structure in which molecules are oriented in the thickness direction of the film, a film is formed on an oxide substrate with good water wettability (also called hydrophilic) such as a glass substrate or an alumina substrate. Curing on the substrate is preferred.

The curing temperature in the curing step can be set according to the components of the epoxy resin composition. For example, it is preferably 200° C. or less, more preferably 180° C. or less. The curing time is not particularly limited, and is preferably 1 to 5 hours, more preferably 2 to 4 hours. It is also preferable to further heat-treat the cured epoxy resin film (hereinafter also referred to as “post-curing”). Post-curing tends to further improve the crosslink density. Thus, the heat treatment may be performed twice or more.

A heating device used for the heat treatment is not particularly limited, and a commonly used heating device can be used. The post-curing temperature is not particularly limited, and is preferably 60°C to 100°C, more preferably 80°C to 100°C. The post-curing time is not particularly limited, and is preferably 10 to 600 minutes, more preferably 60 to 300 minutes.

EXAMPLES The present invention will be specifically described below by way of examples, but the present invention is not limited to these examples. "Parts" and "%" are based on mass unless otherwise specified.

(Example 1)
Liquid crystalline epoxy monomer (4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl=4-(2,3-epoxypropoxy)benzoate, monomer represented by general formula (I), hereinafter referred to as "Resin 1 ”) and 4,4′-biphenol are pre-reacted (hereinafter also referred to as “resin 2”), and a curing agent (3,3′-diaminodiphenylsulfone) is added to prepare an epoxy resin. A composition was prepared. The content of the liquid crystalline epoxy monomer was about 35% by volume in the total solid content of the epoxy resin composition.
Note that the synthesis process of the resin 2 will be described later.

The amounts of the liquid crystalline epoxy monomer and the curing agent are adjusted so that the ratio of the number of equivalents of active hydrogen in the curing agent to the number of equivalents of the epoxy group in the liquid crystalline epoxy monomer (epoxy group:active hydrogen) is 1:1. bottom.
The prepared epoxy resin composition was spin-coated onto a glass substrate at 90° C. and 2000 rpm. After curing the epoxy resin composition by curing at 150° C. for 4 hours, a cured epoxy resin film was obtained by etching the glass substrate with hydrofluoric acid.
The thermal diffusivity of the obtained epoxy resin cured film was measured using a thermal diffusivity measuring device TA3 manufactured by Bethel, and the measurement result was multiplied by the density measured by the Archimedes method and the specific heat measured by the DSC method. , the thermal conductivity in the thickness direction of the cured epoxy resin film was determined. The presence or absence of a liquid crystal structure in the epoxy resin cured film and the alignment direction were examined using Nikon Corporation's product name: "OPTIPHOT2-POL". The average thickness of the cured epoxy resin film was examined using a micrometer. Table 1 shows the results obtained.

<Synthesis of Resin 2>
50 g of Resin 1 was weighed into a 500 mL three-necked flask, and 80 g of propylene glycol monomethyl ether was added as a solvent. A condenser tube and a nitrogen inlet tube were installed in the three-necked flask, and a stirring blade was attached so that the flask was immersed in the solvent. This three-necked flask was immersed in a 120° C. oil bath and stirring was started. After confirming that the resin 1 was dissolved and became a transparent solution, 4,4'-biphenol was added so that the equivalent ratio of the epoxy group and the hydroxyl group (epoxy group/hydroxyl group) was 100/25, 0.5 g of triphenylphosphine was added as a reaction catalyst, and heating was continued at an oil bath temperature of 120°C. After continuing heating for 3 hours, propylene glycol monomethyl ether was distilled off from the reaction solution under reduced pressure, and the residue was cooled to room temperature (25°C), whereby a part of Resin 1 reacted with 4,4'-biphenol. A liquid crystalline epoxy monomer (resin 2) in the form of a polymer (prepolymer) was obtained.

(Example 2)
Example 1 was repeated except that hydroquinone was used instead of 4,4'-biphenol to synthesize a prepolymer (hereinafter also referred to as "resin 3"). The content of the liquid crystalline epoxy monomer was about 35% by volume in the total solid content of the epoxy resin composition.

(Example 3)
In Example 1, instead of Resin 1, a liquid crystalline epoxy monomer (1-(3-methyl-4-oxiranylmethoxyphenyl)-4-(4-oxiranylmethoxyphenyl)-1-cyclohexene) (hereinafter , also referred to as "resin 4") was used to synthesize a prepolymer (hereinafter also referred to as "resin 5"). The content of the liquid crystalline epoxy monomer was about 35% by volume in the total solid content of the epoxy resin composition.

(Example 4)
Example 2 was carried out in the same manner as in Example 2, except that resin 4 was used instead of resin 1 to synthesize a prepolymer (hereinafter also referred to as "resin 6"). The content of the liquid crystalline epoxy monomer was about 35% by volume in the total solid content of the epoxy resin composition.

(Example 5)
Example 1 was repeated except that 100 parts of a solvent (tetrahydrofuran) was added to 100 parts of Resin 2 to prepare an epoxy resin composition.

(Example 6)
In Example 2, the procedure was the same as in Example 2, except that 100 parts of a solvent (tetrahydrofuran) was further added to 100 parts of Resin 3 to prepare an epoxy resin composition.

(Example 7)
In Example 3, the procedure was the same as in Example 3, except that 100 parts of a solvent (tetrahydrofuran) was added to 100 parts of Resin 5 to prepare an epoxy resin composition.

(Example 8)
Example 4 was carried out in the same manner as in Example 4, except that 100 parts of a solvent (tetrahydrofuran) was added to 100 parts of Resin 6 to prepare an epoxy resin composition.

(Comparative example 1)
In Example 1, instead of resin 2, a non-liquid crystalline epoxy monomer (manufactured by Mitsubishi Chemical Corporation: jER828, different from general formula (I)) (hereinafter also referred to as "resin 7") was substituted. Same as Example 1.

(Comparative example 2)
Example 1 was the same as Example 1, except that the spin coating speed was 200 rpm.

(Comparative Example 3)
Except that in Example 1, instead of the glass substrate, a release film (manufactured by DuPont, Melinex S (trade name)) was spin-coated and then physically peeled off after curing to obtain a cured epoxy resin film. was the same as in Example 1.

"-" in the column of prepolymerization agent in Table 1 indicates that prepolymerization was not performed.
"-" in the solvent column in Table 1 indicates that no solvent was used.

As shown in Table 1, Comparative Example 1 does not form a liquid crystal structure because it uses a non-liquid crystalline epoxy resin, and is considered to have low thermal conductivity. It is considered that Comparative Example 2 has a low thermal conductivity due to the thick film thickness. It is considered that Comparative Example 3 has low thermal conductivity in the film thickness direction because the molecules are horizontally oriented.
On the other hand, Examples 1 to 8 form a liquid crystal structure in which the molecules are oriented in the vertical direction (thickness direction of the film) and are considered to have high thermal conductivity due to the thin film thickness.

All publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. incorporated herein by reference.

Claims (11)

A semi-cured epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent,
The liquid crystalline epoxy monomer contains a monomer represented by the following general formula (I),
an average thickness of less than 8 μm,
An epoxy resin B-stage film which, when cured, has a liquid crystal structure in which the molecules are oriented in the direction of film thickness.

[In general formula (I), R ¹ to R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ] 2. The epoxy resin B-stage film according to claim 1 , wherein the liquid crystalline epoxy monomer contains a reaction product of the monomer represented by the general formula (I) and at least one selected from the group consisting of hydroquinone and biphenol. . 3. The epoxy resin B-stage film of Claim 1 or Claim 2, wherein the curing agent comprises an amine curing agent. A cured epoxy resin film comprising a liquid crystal structure in which molecules are oriented in the thickness direction of the film and having an average thickness of less than 8 μm, wherein the liquid crystal structure is a nematic structure or a smectic structure . 5. The epoxy resin cured film according to claim 4 , which is a cured product of an epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent. and a monomer represented by the following general formula (I) as a liquid crystalline epoxy monomer that contains a liquid crystal structure in which molecules are oriented in the thickness direction of the film, has an average thickness of less than 8 μm, and is capable of forming a cured product containing a liquid crystal structure. , a curing agent, and a cured epoxy resin film, which is a cured product of an epoxy resin composition.

[In general formula (I), R ¹ ～R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ] 7. The cured epoxy resin film according to claim 6, wherein the liquid crystal structure is a nematic structure or a smectic structure. 8. The epoxy according to claim 6 or 7, wherein the liquid crystalline epoxy monomer contains a reaction product of the monomer represented by the general formula (I) and at least one selected from the group consisting of hydroquinone and biphenol. Resin cured film. The epoxy resin cured film according to any one of claims 5 to 8 , wherein the curing agent contains an amine curing agent. The epoxy resin cured film according to claim 4 , which is a cured product of the epoxy resin B stage film according to any one of claims 1 to 3. forming a film having an average thickness of less than 8 μm at 150° C. or less using an epoxy resin composition containing a liquid crystalline epoxy monomer capable of forming a cured product having a liquid crystal structure and a curing agent;
curing the film at a curing temperature of 200° C. or less;
has
A method for producing a cured epoxy resin film, wherein the liquid crystalline epoxy monomer contains a monomer represented by the following general formula (I) .

[In general formula (I), R ¹ to R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ]